This application relates to a process for preparing a layered silicate from a reactive form of silica which has been freshly prepared from a solution of a silicate.
Published European Patent Application No. 202,797, the entire disclosure of which is expressly incorporated herein by reference, describes a particular method for the preparation of zeolites such as ZSM-5. According to this method, silica, which has been freshly prepared from a solution of a silicate, is used in the reaction mixture.
Layered silicates such as magadiite are layered materials which have structures distinct from zeolite structures such as that of ZSM-5. Layered materials have three-dimensional structures which exhibit their strongest chemical bonding in only two dimensions. In such materials, the stronger chemical bonds are formed in two-dimensional planes and a three-dimensional solid is formed by stacking such planes on top of each other. However, the interactions between the planes are weaker than the chemical bonds holding an individual plane together. The weaker bonds generally arise from interlayer attractions such as Van der Waals forces, electrostatic interactions, and hydrogen bonding. In those situations where the layered structure has electronically neutral sheets interacting with each other solely through Van der Waals forces, a high degree of lubricity is manifested as the planes slide across each other without encountering the energy barriers that arise with strong interlayer bonding. Graphite is an example of such material. The silicate layers of a number of clay materials are held together by electrostatic attraction mediated by ions located between the layers. In addition, hydrogen bonding interactions can occur directly between complementary sites on adjacent layers, or can be mediated by interlamellar bridging molecules.
The Zones U.S. Pat. No. 4,626,421, the entire disclosure of which is expressly incorporated herein by reference, describes the preparation of magadiite from reaction mixtures containing hydrocarbon substituted ureas or amides. It is pointed out that magadiite is useful as a source of silica for preparation zeolites. In Example 1 of this Zones patent, a sodium silicate solution is used as the source of silica for preparing magadiite. It is stated that there is no gelatin or precipitation of the reaction mixture prior to loading it into the crystallization reactor.
Published European Patent Application No. 205,711 points out that layered oxide materials including layered silicates, such as magadiite and kenyaite, may be intercalated with polymeric oxides to provide catalysts suitable for various hydrocarbon conversions.